A. Technical Field
The present invention relates to an aqueous polymer dispersion, a production process therefor, and an aqueous release agent, and more specifically, relates to: for example, an aqueous release agent, an aqueous blocking-resisting agent, an aqueous smoothing agent, and an aqueous water repelling agent, which are used for paper or various plastic base materials such as poly(vinyl chloride) and polyolefins, particularly, an aqueous release agent which is favorably used to protect or preserve a pressure sensitive adhesive product having a coat of a pressure sensitive adhesive; an aqueous polymer dispersion for producing the aqueous release agent; and a production process for the aqueous polymer dispersion.
B. Background Art
In pressure sensitive adhesive products such as pressure sensitive adhesive tapes and sheets, generally, a release sheet is attached to an adhesive face, or the pressure sensitive adhesive product is wound into a roll to attach the adhesive face to the back face of a carrier, for the purpose of protecting the adhesive face. A release agent is coated onto a release face of the release sheet or onto the back face of the carrier, for the purpose of obtaining good releasibility when being used.
Silicone release agents, or release agents comprising polymers with long-chain hydrocarbon groups such as long-chain alkyl groups (which hereinafter might be referred to as "long-chain alkyl release agents" for briefness), have been proposed as the above release agents so far. In recent years, attention is attracted to the long-chain alkyl release agents among them, because the long-chain alkyl release agents have more excellent re-adhesion, writability, and printability than the silicone release agents. JP-B-40-017661 proposes a pressure sensitive adhesive product in which a polymer as obtained by grafting an alkyl isocyanate upon polyethylenimine is used as a solvent type release agent.
Furthermore, JP-A-03-050279, JP-A-03-086776, and JP-03-086777 propose arts to make the long-chain alkyl release agent aqueous, considering the work environment or the environmental pollution. That is to say, these are arts in which an aqueous dispersion of a long-chain alkyl grafted polymer is obtained by a specific process comprising the step of reacting raw materials under stirring in water, or post-emulsifying a polymer, and the resultant aqueous dispersion is used as the release agent.
The aqueous release agents comprising aqueous dispersions of long-chain alkyl grafted polymers, as proposed in the above prior arts, exhibit excellent releasibility at normal temperature in respect to having little release resistance and not deteriorating the adhesion of the pressure sensitive adhesive layer. However, the above conventional aqueous release agents have problems of heat resistance in that, after being preserved at high temperature in a state of being attached to the adhesive face, they easily transfer to the pressure sensitive adhesive layer, so the adhesion of the pressure sensitive adhesive layer deteriorates or the release force increases. In addition, especially in the case where the drying temperature of the release agent during the formation of the release agent layer is a low temperature of not higher than 100.degree. C., there are also problems in that the release agent layer easily becomes white turbid, so the transparency of the pressure sensitive adhesive product is damaged due to the release agent when a transparent carrier is used.